The influence of nozzle-exit geometric profile on statistical properties of a turbulent plane jet

Abstract

The paper reports an investigation of the influence of geometric profile of a long slot nozzle on the statistical properties of a plane jet discharging into a large space. The nozzle-exit profile was varied by changing orifice-plates with different exit radii ( r) over the range of 0 < r/ h < 3.60, where h is the slot-height. The present measurements were made at a slot-height based Reynolds number ( Re h ) of 1.80 × 10 4 and a slot aspect ratio (span/height) of 72. The results obtained show that both the initial flow and the downstream flow are dependent upon the ratio r/ h. A “top-hat” mean exit velocity profile is closely approximated when r/ h approaches 3.60. The decay and spread rates of the jet’s mean velocity decrease asymptotically as r/ h is increased, with the differences becoming small as r/ h approaches 3.60. A decrease in r/ h results in a higher formation rate of the primary vortices in the near-field. The far-field values of the centerline turbulence intensity are higher for smaller r/ h, and display asymptotic-like convergence as r/ h approaches 3.60. Overall, the effect of r/ h on the mean and turbulence fields decreases as r/ h increases.